Spark ignition systems for internal combustion engines



y 6, 1967 B. GILBERT 3,319,617

SPARK IGNITION SYSTEMS FO R INTERNAL COMBUSTION ENGINES Filed Nov. 22, 1963 United States Patent Ofifice 3 $19,617 Patented May 16, 1967 This invention relates to spark ignition systems for internal combustion engines, of the kind in which current flow in a winding controls the discharge across a spark plug of the engine.

The winding may be the primary winding of a transformer having the plug in its secondary circuit. However, where low-voltage plugs are used the plug may be fed from the winding.

The present invention makes use of a device known as a controlled rectifier, the characteristic of which is that if a triggering pulse is applied between its gate and cathode terminals the rectifier becomes conductive, and thereafter continues to conduct, even when the triggering pulse is removed, until the anode-cathode current falls to zero. Furthermore, it has recently been discovered that controlled rectifiers manufactured in a certain manner have the additional property that they can be switched oif by a pulse of opposite polarity (but not necessarily of equal magnitude) applied between the gate and cathode. Throughout this specification the term switchable rectifier is used to mean a controlled rectifier having this additional property.

A spark ignition system of the kind specified and according to the invention comprises in combination first and second terminals for connection to a DC. source, a switchable rectifier having its anode and cathode connected across said terminals in series with said winding, a series circuit connected across said terminals, said series circuit including a contact breaker and an inductor, means coupling said series circuit to the gate of the switchable rectifier, so that the switchable rectifier is switched on when the contact breaker closes, and is switched off by the energy stored in the inductor when the contact breaker opens, a first capacitor connected across the contact breaker, and an additional capacitor connected in the system, said additional capacitor being connected in a position such that in the event of the contact breaker reaking down after it opens, the charge on this additional capacitor will prevent inadvertent switching on of the switchable rectifier.

In the accompanying drawings, FIGURE 1 is a circuit diagram showing an arrangement having certain disadvantages, FIGURE 2 shows one example of a circuit for minimising such disadvantages, and FIGURES 3 and 4 illustrate further examples.

Referring to FIGURE 1, there are provided first and second terminals 11, 12 which in use are connected to a DC. source 13 so as to be of positive and negative polarity respectively. There is further provided an ignition transformer 14 having its secondary winding 15 connected through a distributor 16 to the spark plugs 17 of the engine in turn.

The primary winding 18 of the transformer 14 has one end connected through a resistor 19 to the terminal 11, and its other end connected to the terminal 12 through the anode and cathode of a switchable rectifier 21, the anode and cathode being bridged by a capacitor 22. Moreover connected between the terminals 11, 12 is a series circuit including a contact breaker 23, a resistor 24 and an inductor 25. The contact breaker 23 is bridged by a capacitor 26, whilst a point 27 intermediate the resistor 24 and inductor 25 is connected to the gate of the switchable rectifier 21.

The circuit thus far described operates in the following manner: when the contact breaker 23 closes, current flows from terminal 11 through the contact breaker 23 and resistor 24 to the point 27 between the resistor 24 and inductor 25. From the point 27, part of the current flows 7 to the terminal 12 through the gate and cathode of the rectifier 21, so switching the rectifier 21 on. The remainder of the current flows to the terminal 12 through the inductor 25, in which energy is stored.

When the contact breaker 23 opens, a back is induced in the inductor 25 causing the point 27 to become negative with respect to the terminal 12. Current flows from the point 27 through the gate and cathode I l of the rectifier 21 to switch it off. At the same time, the

capacitor 26 is charged so that its lower plate is negative.

Whilst the rectifier 21 is conducting, current flows in the winding 18. However, when the rectifier 21 is switched off, the fall in current through the winding 18 produces a large voltage in the Winding 15, which results in a spark being produced at one of the plugs of the engine. The contact breaker 23 and distributor 16 are driven by the engine in timed relationship so that sparks are produced at the plugs of the engine in turn. The

'1 rectifier 21 is protected against the effect of back in winding 18 by the capacitor 22.

With the circuit described, there is a possibility that the voltage across the capacitor 26 will cause sparking between the contacts of the contact breaker 23 after the This sparking may occur once or several times. Provided the sparking stops before the switchable rectifier 21 is switched ofi, it has no major deleterious effect, but if a spark occurs at the contacts after the switchable rectifier has been switched off,

i there is a possibility that the switchable rectifier 21 will be switched on again, particularly as the circuit connecting the capacitor 26 across the contact breaker 23 will probably have an unavoidable inductive component which tends to cause the voltage across the capacitor 26 .to reverse its polarity. Such inadvertent switch-on is clearly undesirable.

It has been found that this unwanted effect can be avoided if the capacitor 26 is in efiect split into two parts.

Thus, whereas in the example shown in FIGURE 1 ther capacitor 26 might be of capacitance 0.2 microfarad, it is replaced as shown in FIGURE 2 by a capacitor 26a connected across the contact breaker 23 and of capacitance 0.05 microfarad, and a further capacitor 26b connected in parallel with the inductor 25, the capacitance of the capacitor 2612 being 0.15 microfarad. The arrangement is such that when the inductor 25 drives point 27 negative, both capacitors are charged to almost equal potentials behaving thus efiectively as a single capacitor. However, if the contact breaker 23 breaks down, the capacitor 26a will discharge in a oscillatory manner in the same way as the capacitor 26 in FIGURE 1, but the capacitor 26b will discharge exponentially through the resistor 24. The constants of the circuit are so chosen that the point 27 cannot become sutficiently positive to switch on the rectifier 21 until the contact breaker 23 closes again.

In the modification of FIGURE 2 shown in FIGURE 3, a diode 28 is included between the inductor 25 and the point 27, and the capacitor 26b is bridged by a resistor 29. The diode 28 prevents re-switching on of the switchable rectifier 21 as a result of oscillations occurring between the inductor 25 and the capacitors 26a, 26b, and the resistor 29 ensures that these capacitors are completely discharged at the end of each cycle before the contact breaker 23 closes.

As well as sparking between the contacts of the contact breaker 23, there may occur actual temporary physical reclosure of the contacts of such duration as to cause the switchable rectifier 21 to switch on again even though the circuit is arranged as described in the example. If such closure should occur before the spark is produced at a plug 17, the spark will be impaired, but it is possible to prevent this from happening by arranging that any inadvertent switch-on is delayed beyond the instant of reclosure of the contacts at least long enough for the voltage across the winding 15 to rise to the value at which the ignition spark is produced. This is conveniently done, without alteration to the energy stored by the inductor 25,by the insertion of a resistor 31 between the point 27 and the gate of the rectifier 21. Preferably the resistor 31 is in parallel with a diode 32 connected so that the switch 011 pulse is not impeded. 7

FIGURE 4 illustrates two alternative positions for the capacitor 26b. In the full line position, the capacitor 26b is connected across the capacitor 26a is series with a resistor 33. In the dotted line position, the capacitor 26b is connected between the terminal 11 and point 27.

The operation is similar to the circuit shown in FIGURE 2. Moreover, a resistor maybe included in series with the capacitor 26b in FIGURE 2, or the capacitor 26b shown in dotted lines in FIGURE 4.

In all examples so far described, the point 27 has been connected to the gate of the switchable rectifier 21 either directly or through a resistor. However, the coupling to the gate of the switchable rectifier can be inductive, and for this purpose the inductor may constitute the primary winding of a transformer, the secondary winding of which has one end connected to the terminal 12 and its other end connected to the gate of the rectifier 21.

Having thus described my invention what I claim as new and desire to secure by Letters Patent is:

1. A spark ignition system for an internal combustion engine, of the kind in which current flow in a winding controls discharge across a spark plug of the engine, comprising in combination a DC. source having a positive terminal and a negative terminal, a switchable rectifier having its anode and cathode connected across said terminals in series with said winding, said switchable rectifier having an anode, a cathode and a gate, and being turned on by a positive pulse between its gate and cathode, and turned off by a negative pulse between its gate and cathode, a series circuit connected across said terminals, said series circuit including a contact breaker having one side thereof connected to said positive terminal and an inductor through which the other side of said contact breaker is connected to said negative terminal, means coupling a point in said series circuit intermediate the contact breaker and inductor to the gate of the switchable rectifier, so that the switchable rectifier point intermediate the inductor and contact breaker and the negative terminal.

3. A spark ignition system as claimed in claim 1 in which the additional capacitor is connected between a point intermediate the inductor and contact breaker and the positive terminal.

4. A spark ignition system as claimed in claim 1 including a resistor in series with the additional capacitor.

5. A spark ignition system as claimed in claim 1 in which the additional capacitor is connected across the first capacitor in series with a resistor.

6. A spark ignition system as claimed in claim 1 in which the series circuit includes a resistor and a diode in series between the contact breaker and the inductor,

the diode preventing the inductor and additional capacitor from forming an oscillatory circuit.

7. A spark ignition system as claimed inclaim 6 including a resistor connected between the negative terminal and a point intermediate the diode and resistor in the series circuit.

8. A spark ignition system as claimed in claim 6 in which said means coupling the series circuit to the gate comprises a connection from the gate to a point intermediate the diode and resistor in the series circuit.

9. A spark ignition system as claimed in claim 8 in which said connection includes a resistor which delays switching on of the switchable rectifier.

10. A spark ignition system as claimed in claim 9 including a diode connected across said resistor so that switching 011 of the switchable rectifier is not delayed.

References Cited by the Examiner UNITED STATES PATENTS 2,011,395 8/1935 Cain. 2,433,650 12/1947 Coe et a1. 3,025,430 3/ 1962 Leppala. 3,131,327 4/1964 Quinn 123-148 X 3,213,320 10/1965 Worrell. 3,219,877 11/1965 Konopa.

MARK NEWMAN, Primary Examiner.

LAURENCE M. GOODRIDGE, Examiner. 

1. A SPARK IGNITION SYSTEM FOR AN INTERNAL COMBUSTION ENGINE, OF THE KIND IN WHICH CURRENT FLOW IN A WINDING CONTROLS DISCHARGE ACROSS A SPARK PLUG OF THE ENGINE, COMPRISING IN COMBINATION A D.C. SOURCE HAVING A POSITIVE TERMINAL AND A NEGATIVE TERMINAL, A SWITCHABLE RECTIFIER HAVING ITS ANODE AND CATHODE CONNECTED ACROSS SAID TERMINALS IN SERIES WITH SAID WINDING, SAID SWITCHABLE RECTIFIER HAVING AN ANODE, A CATHODE AND A GATE, AND BEING TURNED ON BY A POSITIVE PULSE BETWEEN ITS GATE AND CATHODE, AND TURNED OFF BY A NEGATIVE PULSE BETWEEN ITS GATE AND CATHODE, A SERIES CIRCUIT CONNECTED ACROSS SAID TERMINALS, SAID SERIES CIRCUIT INCLUDING A CONTACT BREAKER HAVING ONE SIDE THEREOF CONNECTED TO SAID POSITIVE TERMINAL AND AN INDUCTOR THROUGH WHICH THE OTHER SIDE OF SAID CONTACT BREAKER IS CONNECTED TO SAID NEGATIVE TERMINAL, MEANS COUPLING A POINT IN SAID SERIES CIRCUIT INTERMEDIATE THE CONTACT BREAKER AND INDUCTOR TO THE GATE OF THE SWITCHABLE RECTIFIER, SO THAT THE SWITCHABLE RECTIFIER IS SWITCHED ON WHEN THE CONTACT BREAKER CLOSES, AND IS SWITCHED OFF BY THE ENERGY STORED IN THE INDUCTOR WHEN THE CONTACT BREAKER OPENS, A FIRST CAPACITOR CONNECTED ACROSS THE CONTACT BREAKER, AND AN ADDITIONAL CAPACITOR CONNECTED IN THE SYSTEM, SAID ADDITIONAL CAPACITOR BEING CONNECTED IN A POSITION SUCH THAT IN THE EVENT OF THE INTERRUPTER BREAKING DOWN AFTER IT OPENS, THE CHARGE ON THIS ADDITIONAL CAPACITOR WILL PREVENT INADVERTENT SWITCHING ON OF THE SWITCHABLE RECTIFIER. 